Forget the Burn. Go for the Shake.The Workout4) Back Builder

Drop down on all fours (like a cat) with equal weight on your knees and hands. Bring one arm forward while keeping your torso still and your eyes on the floor. Lift your opposite leg out behind you and hold, while keeping your pelvis steady. Tighten your abs and lengthen your hand forward and your foot back. Repeat on the other side; do five reps on each side.

For the Shake:

Slowly lift your extended arm and leg up and down in tiny pulses when extended.